has anyone else had this experience?

So I miscarried at the very beginning of february. doctors told me to take a test at 3 weeks and to come back if still positive. I tested, and negative. fast forward to last week and my man told me to take a test and boom, I’m pregnant with my rainbow baby. So I went for a pregnancy confirmation at my ob and the doctor estimated my pregnancy to be 19 weeks? She told me that by next week if I have any bleeding or anything to go to labor and delivery. I feel like this is so misleading? like why wouldn’t you just wait for my ultrasound to give me an estimate like that. she made it seem like I may have had vanishing twin syndrome but I had an ectopic pregnancy, and saw nothing in the ultrasound. so how did this baby just come out of nowhere? I don’t even feel 19 weeks like what-